Introduction Copper quotas (QCu) of phytoplankton are maintained within narrow limits by cellular regulatory processes even as environmental concentrations vary by orders of magnitude (Sunda and Huntsman, 1995; Page et al., 2009). The quotas are set by the amounts of Cu-redox proteins required in cellular metabolism (Merchant et al., 2006; Kim and Price, 2017; Kong and Price, 2022) and depend upon uptake of Cu from the environment.